This is not strictly a brass instrument, but it is an early bass/baritone instrument made of wood covered with animal hide. It is essentially a conical tube with holes inserted to enable different pitch notes to be played.  The connection to brass instruments is the fact that a mouthpiece was used with the players lips making the necesary vibrations to the air column (lip vibrated aerophone).  To make it possible for the player's hands to reach these holes, the Serpent is wound up as shown.  This example is particularly convoluted!